pipe: Add notification lossage handling

Add handling for loss of notifications by having read() insert a
loss-notification message after it has read the pipe buffer that was last
in the ring when the loss occurred.

Lossage can come about either by running out of notification descriptors or
by running out of space in the pipe ring.

Signed-off-by: David Howells <dhowells@redhat.com>

1 files changed, 2 insertions, 0 deletions

diff --git a/kernel/watch_queue.c b/kernel/watch_queue.c
index ad64ea300f6d..9a9699c06709 100644
--- a/kernel/watch_queue.c
+++ b/kernel/watch_queue.c
@@ -132,6 +132,8 @@ out:
 	return done;
 
 lost:
+	buf = &pipe->bufs[(head - 1) & mask];
+	buf->flags |= PIPE_BUF_FLAG_LOSS;
 	goto out;
 }